A vehicle is subject to some degree of disturbance in its front road wheels (e.g., road-wheel imbalance). This disturbance can cause undesirable vibrations in the steering wheel or handwheel detectable by a driver. These vibrations are directly related to the rotational mean velocity of the road wheels. The severity of the vibrations at the handwheel depends upon both the magnitude of the disturbance and the chassis and steering design.
Methods have been employed to reduce handwheel vibrations due to road-wheel disturbance. One method is to reduce the source of the disturbance. However, this approach has practical limitations. For example, in the case of road-wheel imbalance, there are changes in the imbalance over tire and wheel wear.
Another method is to minimize transmissibility of the disturbance to the driver. The transmissibility is affected by physical design of the chassis and steering system and tuning of the steering system. However, there are limitations to such minimization because of trade-offs with other design considerations.
In vehicles equipped with electric-power steering (EPS), another method is to minimize transmissibility of road-wheel imbalance—namely, targeted algorithms are specifically aimed at rejecting disturbance due to road-wheel imbalance. With such an approach, it is possible to reject the disturbance with minimal impact on other performance aspects of the system. In vehicles equipped with hydraulic-power steering (HPS), the transmissibility may be minimized through mechanical methods, such as selection of torsional stiffness of T-bars, increased friction, and mounting stiffness.